Reflow soldering ovens are used in the production of printed circuit boards employing surface mount technology. Typically, in a reflow soldering oven, the products to be soldered pass through heating zones to a cooling zone. The heating zones are separated into a number of different zones which are generally broken down into preheat zones, soak zones and spike zones. In the preheat zones and the soak zones, the products are heated and the flux volatile components vaporize in the surrounding gas atmosphere. The spike zones are hotter than the preheat zones and soak zones, and it is in the spike zones that the solder melts. A reflow solder oven may have many heating zones and these heating zones can be varied depending on the products to be soldered. Different products require different heat profiles and a solder oven should be flexible so that, for example, a machine with ten heating zones may have one preheat zone followed by seven soak zones and two spike zones for one type of circuit board, and a machine may have three preheat zones, six soak zones and one spike zone for a different type of board. The cooling zone or zones follow the heating zones and are used to solidify the solder on the board.
During production, a paste containing solder particles mixed with flux, adhesives, binders, and other components is applied to selected areas of a printed circuit board. Electronic components are pressed against the applied solder paste, while adhesives in the paste hold the components to the printed circuit board. A conveyor belt within a reflow oven carries the printed circuit board and components through a high temperature region within the oven where they are heated to a temperature sufficient to cause the solder particles in the paste to melt. Molten solder wets metal contacts on the components and printed circuit board. The flux in the solder paste reacts with the contacts to remove oxides and to enhance wetting. The conveyor belt moves the heated printed circuit board to a cooling region of the oven where the molten solder solidifies forming a completed electronic circuit.
The reaction of the flux with the contacts liberates vapors. Further, heat within the oven vaporizes un-reacted flux as well as the adhesives, binders, and other components of the solder paste. If the vapors migrate to the cooling region, they can undesirably condense on the circuit boards. The vapors may also condense on cooler surfaces within the oven.
The vapors generated by the reflow operation collectively are referred to herein as “flux vapors.” It is understood that the flux vapors can include vaporized flux, vapors from other components of the solder paste, reaction products released when the flux is heated, as well as vapors out-gassed from the printed circuit board and electronic components.
It is therefore desirable to provide a flux management system that removes flux from the system while preventing or minimizing flux from dripping on the printed product. It is also desirable to provide a flux management system that can be cleaned with little or minimized maintenance downtime for the associated reflow oven.